Psychological Effects of Levodopa in Parkinson's Disease

Parkinson's disease (PD) is primarily classified and known as a movement disorder characterized by tremor, bradykinesia and rigidity. However, clinical examination and research have shown that PD extensively affects other systems as well, giving rise to non-motor symptoms (NMS) such as anxiety, sleep disorders, apathy, depression, cognitive impairment, and hallucinations. These non-motor fluctuations (NMF) represent a main source of disability in PD and among those, neuropsychiatric fluctuations are the most frequent. During the dopaminergic OFF-drug state anxiety, apathy, and depression are common, whereas during the dopaminergic ON-drug state euphoria, well-being, impulse control disorders (ICD) and other behavioral addictions, mania, and psychosis might occur. Despite the severe consequences associated with dopaminergic modulation, the understanding of the pathophysiological mechanisms of neuropsychiatric symptoms is still limited and better detection and more effective treatments are needed. Fluctuating PD is a very powerful model allowing to study opposite psychiatric states intra-individually in both levodopa dopaminergic ON- and OFF-drug state, allowing to abstract many interpersonal variables. Neurotechnology and advanced neuroimaging techniques can improve the understanding of the neural basis and brain mechanisms of specific neuropsychiatric symptoms in PD. In particular, dynamic functional connectivity (FC) analysis characterizes functional abnormalities from resting state (rs)-fMRI not only in terms of brain activations, but also of whole-brain functional networks and the transitions between maps of activations. The temporal evolution of these networks, assessed with dynamic FC approaches, has recently shown to be relevant in several clinical contexts. Therefore, the investigators long-term goal is to identify specific resting-state signatures/biomarkers for the individual neuropsychiatric PD symptoms related to disease in dopaminergic OFF-drug state (depression, anxiety, apathy, fatigue, shame, bradyphrenia) and to dopaminergic treatment in dopaminergic ON-drug state (mania, impulse control disorders, hallucinations, psychosis, creative thinking), which might be used in the future as a proxy for the measurement of neuropsychiatric symptoms/fluctuations and thus to assess the effectiveness of specific therapies.